Blood oxygen saturation is one of many parameters used to assess a patient's health, and in particular, the efficacy of their circulation and cardiovascular system. Oxygen saturation can be directly measured via invasive methods, e.g., by taking a sample of blood from the patient. However, portable oximetry systems allow non-invasive blood oxygen saturation measurement via reflectance or absorption measurements performed on or through a patient's skin or nailbeds, for example. Some oximetry systems determine blood oxygen saturation from the absorption of light by oxy- or deoxyhemoglobin in a tissue sample area.